Regulated single-ended self oscillating, DC-DC converter

Abstract

A switching regulator having a blocking oscillator including a transistor, and a transformer with primary, secondary, and positive feedback windings. A rectifying and smoothing circuit is connected to the load and includes a photodiode coupled to a phototransistor connected to the blocking oscillator transistor in the feedback path for adjusting feedback to maintain output voltage at a constant level. A second positive feedback circuit connects between the phototransistor and the blocking oscillator transistor to assure stable oscillation of the blocking oscillator.

What is claimed is: 
     
       1. A switching regulator comprising: an oscillator including a first transistor and a transformer having a primary winding connected to said transistor, a secondary winding and a positive feedback winding connected to said transistor,   a rectifying and smoothing circuit connected to said secondary winding,   excessive voltage detecting means for detecting that the output voltage of the rectifying and smoothing circuit has exceeded a predetermined value,   a second transistor connected to said first transistor for controlling the duration of conduction of the first transistor by detecting the excessive voltage, and   a positive feedback circuit connected between the collector of the first transistor and the base of the second transistor for stabilizing the oscillation of the oscillator.   
     
     
       2. A switching regulator as defined in claim 1 which further comprises means for detecting an excessive current through the oscillator, and the duration of conduction of the three-terminal control element is controlled also by detecting the excessive current. 
     
     
       3. A switching regulator as defined in claim 1 wherein the excessive voltage detecting means includes a light emitting diode which emits light when the output voltage of the rectifying smoothing circuit exceeds a predetermined value, the second transistor is a phototransistor connected to the base of the first transistor and wherein the light emitting diode and the phototransistor constitute a photocoupler. 
     
     
       4. A switching regulator comprising: a blocking oscillator including a transistor and a transformer having a primary winding connected to said transistor, a secondary winding and a positive feedback winding constituting a positive feedback circuit for the transistor,   a rectifying and smoothing circuit connected to the secondary winding of the transformer,   an excessive voltage detecting circuit including a light emitting diode for detecting the output voltage of the rectifying and smoothing circuit has exceeded a predetermined value whereupon a current flows through the light emitting diode, and   a control element connected to said transistor and said excessive voltage detecting circuit for controlling the duration of conduction of the transistor of the blocking oscillator by detecting the excessive voltage,   a bias circuit connected to the control element   wherein the control element is a phototransistor connected to the base of the transistor of the blocking oscillator, and   wherein the light emitting diode and the phototransistor constitute a photocoupler.   
     
     
       5. A switching regulator as defined in claim 4 which further comprises a circuit for detecting an excessive current through the blocking oscillator, the phototransistor having a base terminal, the base of the phototransistor being controllable by an excessive current detecting signal. 
     
     
       6. A switching regulator as defined in claim 4 wherein the phototransistor has a base terminal, and a differentiating circuit is provided for positively feeding back the collector voltage of the transistor of the blocking oscillator or the voltage induced in the positive feedback winding of the transformer to the base of the phototransistor. 
     
     
       7. A switching regulator as defined in claim 4 which further comprises a voltage drop element connected between the control element and the base of the transistor of the blocking oscillator. 
     
     
       8. A switching regulator as defined in claim 4 which further comprises a Zener diode connected between the bias circuit and the base of the transistor of the blocking oscillator.